4-Hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine and 4-oxo-1-oxyl-2,2,6,6-tetramethylpiperidine are reported to have been used to trap carbon centered radicals formed from methanol, ethanol, isopropanol and sec-butanol by S. Nigam et al., J. Chem. Soc., Trans. Faraday Soc. 1, 1976, 72, 2324 and by K.-D. Asmus et al., Int. J. Radiat. Biol., 1976, 29, 211.
U.S. Pat. No. 5,627,248 and European Patent Application No. 135,280 A2 describe, respectively, difunctional and monofunctional living free radical polymerization initiators, some of which contain hindered amine ethers substituted by hydroxy groups. These compounds differ substantially in structure and performance from the instant compounds.
European Patent Application No. 427,672 A1 and U.S. Pat. No. 4,972,009 mention, but do not exemplify, respectively, hydroxylamine and nitrone structures, some of which contain C1-C4 hydroxyalkoxy substituted 2,2,6,6-tetramethylpiperidine derivatives. Such structures are outside the scope of the instant invention.
U.S. Pat. No. 5,204,473 describes N-hydrocarbyloxy hindered amine derivatives that are prepared exclusively from organic compounds containing only carbon and hydrogen atoms. Such compounds are structurally quite different from the instant compounds.
U.S. Pat. No. 5,004,770 describes hindered amine compounds which are substituted on the N-atom by alkoxy moieties which alkoxy groups are themselves unsubstituted. These compounds are especially useful in polymers including polybutadiene, polystyrene, ABS, polyacetal, polyamide, polyester, polyurethane and polycarbonate.
U.S. Pat. No. 5,096,950 also describes hindered amine compounds which are substituted on the N-atom by alkoxy moieties which alkoxy groups are themselves unsubstituted. These compounds are found to be useful in polyolefins.
The instant compounds are N-alkoxy substituted derivatives of 2,2,6,6-tetraalkylpiperidines where the alkoxy group is substituted by one to three hydroxy moieties. The instant compounds also comprise N-alkoxy bridged derivatives of the 2,2,6,6-tetraalkylpiperidines where the alkoxy moiety, which is substituted by one to three hydroxy groups, is shared by two hindered amine molecules. The free hydroxy moieties of these compounds may be reacted with carboxylic acids, acid chlorides or esters to form simple esters or polyesters, or with isocyanates to form urethanes or polyurethanes.
The instant compounds, because of their low bascity which is shared by the simple unsubstituted N-alkoxy compounds cited in the two patents mentioned above, are of particular value in the stabilization of polyolefins and automotive coating compositions where the activity of the more basic hindered amine stabilizes is significantly reduced because of interaction with the polymer substrate or acid catalytic system needed for curing such substrate.
Examples of polyolefin compositions in which the instant compounds are effective include flame retardant polyolefins where acidic residues from the decomposition of the halogenated flame retardants deactivate hindered amines not having the N—OR group, greenhouse films and agricultural mulch films where acidic residues from pesticides interfere with the activity of “normal” hindered amine stabilizers, and in thermoplastic polyolefins where pigment interactions with basic hindered amine stabilizers interfere with painting the substrate surfaces. Examples of coating compositions in which the instant compounds are effective include melamine crosslinked thermoset acrylic resins, which are cured-using strong acids that interact with basic hindered amine stabilizers. The instant compounds are also effective in acrylic alkyd or polyester resins with isocyanate crosslinking agents, and in epoxy resins with carboxylic acid, anhydride, or amine crosslinking agents.
While the unsubstituted N—OR compounds described in U.S. Pat. Nos. 5,004,770 and 5,096,950 also perform well in the compositions described in the paragraph above, the instant compounds differ significantly in both structure and in performance from the prior art compounds by virtue of the presence of the one to three free hydroxy groups present on the N-alkoxy moiety. These hydroxyl groups in the instant compounds provide said compounds with superior antistatic properties, compatibility in more polar environments such as polyurethane based and in water-borne automotive coating-systems, and in stabilizing painted automotive thermoplastic olefin structures.
The instant compounds are particularly suited for
(a) providing superior compatibility in polycarbonates and polycarbonate/ABS blends compared to the N—OE prior art compounds; and
(b) providing superior compatibility in polyesters and polyamides compared to the prior art N—OE compounds.